ELECTRONIC-STRUCTURE AND OPTICAL-PROPERTIES OF WO3, LIWO3, NAWO3, ANDHWO3

The electronic structures for cubic WO3, LiWO3, NaWO3, HWO3, H2WO3, an d hexagonal WO3 have been calculated. The calculations rely on the loc al approximation to density functional theory and use a full-potential linear mufin-tin orbitals method. The incorporation of ions in tungst en oxide by chemical or electrochemical methods is the basis for sever al technological applications related to solid state ionics. Essential ly, incorporation of alkali ions results in an s-band high above the F ermi level, and the charge-balancing electrons take part in a rigid ba nd filling of the W d conduction band. Hydrogen forms a hydroxide unit with one oxygen atom, and we find a minimum in total energy for a bon d length of 1.03 Angstrom. The cubic phase of WO3 can take up more tha n one hydrogen atom, and the formation of two hydroxide units is prefe rable to one water molecule. The calculated dielectric function and re flectance of LixWO3 and NaxWO3 are presented, and the change in optica l properties being the basis for reflective electrochromism is reprodu ced, although the reflectance curves show some deviations from experim ents.